Rhombohedral Twin Structure in Hematite (α-Fe2O3)

1992 ◽  
Vol 45 (9) ◽  
pp. 1527 ◽  
Author(s):  
LA Bursill ◽  
JL Peng ◽  
XD Fan
Keyword(s):  
Image Matching ◽  
Structural Models ◽  
Nearest Neighbour ◽  
Twin Structure ◽  
Systematic Analysis ◽  
Coherent Interface ◽  
Pure Rotation ◽  
Twinning Plane ◽  
Twinning Direction ◽  
Edge Shared Octahedra

Electron optical imaging of the structure of haematite ( α-Fe2O3) in two projections has allowed the microscopic twinning elements of rhombohedral twins to be determined. A systematic analysis of alternative structural models, using computer-simulation and image-matching considerations, as well as crystallochemical arguments, is presented. The twin has a screw operation consisting of a pure rotation of 180� about [0111], the twinning direction, combined with a parallel translation of (1/22) [0111]. The twinning plane (0112) forms a coherent interface, consisting of face-and edge-shared octahedra , with no change in the normal nearest-neighbour coordination.

CONSTRAINT-BASED ANALYSIS OF PARALLEL KINEMATIC ARTICULATED WRIST MECHANISM

2021 ◽  
pp. 1-11
Author(s):  
Revanth Damerla ◽  
Shorya Awtar
Keyword(s):  
Degrees Of Freedom ◽  
Systematic Analysis ◽  
Load Bearing ◽  
Load Transmission ◽  
Pure Rotation ◽  
Parallel Kinematic ◽  
Design Tradeoffs ◽  
Transmission Capability

Abstract This paper presents a systematic constraint-based analysis of the performance attributes of eight parallel kinematic articulated wrist mechanisms from the existing literature. These performance attributes include the number, nature (i.e. pure rotation, or translation, or a combination), and location of a mechanism's Degrees of Freedom (DoFs) in the nominal and displaced configurations, load transmission capability along these DoFs, and load bearing capability along the constraint directions. This systematic analysis reveals performance tradeoffs between these performance attributes for a given mechanism, as well as design tradeoffs across these mechanisms. This analysis also helps inform the suitability of a given mechanism for specific applications.

scholarly journals Karakteristik Metode Sift dalam Aplikasi Sistem Pengenalan Motif Batik

MIND Journal ◽  
2019 ◽  
Vol 4 (2) ◽  
pp. 122-131
Author(s):  
MILDA GUSTIANA HUSADA ◽  
DINA BUDHI UTAMI ◽  
IWAN ZAR
Keyword(s):  
Image Matching ◽  
Nearest Neighbor ◽  
Nearest Neighbor Search ◽  
Nearest Neighbour ◽  
Neighbor Search

Pada kajian ini dibahas penerapan CBIR yaitu cara perolehan temu balik (retreival) objek citra melalui proses pembandingan antara citra uji terhadap citra latih yang dikumpulkan dalam suatu database. Proses membandingan citra berlandaskan pada tanda-tanda (ciri) yang dimiliki diantara citra tersebut. Tanda-tanda yang digunakan pada cara CBIR yaitu berdasarkan kemiripan warna, bentuk, dan tekstur. Pada makalah ini metode SIFT digunakan untuk mendapatkan dan mendeskripsikan fitur-fitur lokal yang ada pada citra. Fitur citra latih dan citra uji yang diperoleh kemudian dibandingkan dengan menggunakan Nearest Neighbour Search untuk memperoleh tingkat kemiripan (proses image matching). Pengujian dilakukan pada citra yang diperoleh melalui kamera dan citra yang sudah berupa data digital. Berdasarkan pengujian, nilai precision dan recall untuk citra uji yang diambil melalui kamera berturut-turut adalah 64% dan 12,8%, sedangkan untuk citra uji dari digital dioleh adalah 84% dan 16.8%. Kata kunci: CBIR, SIFT, Image Matching, Nearest Neighbor Search

Analysis on the Twinning of FCC Metals by EBSD

2012 ◽  
Vol 472-475 ◽  
pp. 700-706 ◽  
Author(s):  
Guang Sheng Song ◽  
Shi Hong Zhang ◽  
Ming Cheng ◽  
Bin Wang
Keyword(s):  
Rotation Angle ◽  
Rotation Axis ◽  
Face Centered Cubic ◽  
Practical Application ◽  
Fcc Metals ◽  
Twinning Plane ◽  
Twinning Direction ◽  
Face Centered

For the technology of EBSD, the twinning of metals was described in the form of rotation angle combined with rotation axis, while the twinning of metals was usually described in the form of twinning plane combined with twinning direction. In this report, the corresponding relationship between the two description forms of twinning of face-centered cubic (FCC) metals has been built, based on this relationship, the twinning plane and twinning direction of FCC metals can be determined by EBSD. As the practical application of this relationship above, the twinning variants of two kinds of Ni based superalloys were analyzed.

Constraint-Based Analysis of Parallel Kinematic Articulated Wrist Mechanisms

2020 ◽  
Author(s):  
Revanth Damerla ◽  
Shorya Awtar
Keyword(s):  
Degrees Of Freedom ◽  
Systematic Analysis ◽  
Load Bearing ◽  
Load Transmission ◽  
Pure Rotation ◽  
Parallel Kinematic ◽  
Design Tradeoffs ◽  
Transmission Capability

Abstract This paper presents a systematic constraint-based analysis of the motion attributes of six parallel kinematic articulated wrist mechanisms from the existing literature. These motion attributes include the number, nature (i.e. pure rotation, or translation, or a combination), and location of mechanism’s Degrees of Freedom (DoFs) in the nominal and displaced configurations, range of operation along these DoFs, load transmission capability along these DoFs, and load bearing capability along the constraint directions. This systematic analysis reveals performance tradeoffs between these motion attributes for a given mechanism, as well as design tradeoffs across these multiple mechanisms with respect to these motion attributes. This analysis should help inform the suitability of a given mechanism for specific applications.

scholarly journals A general method to determine twinning elements

2010 ◽  
Vol 43 (6) ◽  
pp. 1426-1430 ◽  
Author(s):  
Yudong Zhang ◽  
Zongbin Li ◽  
Claude Esling ◽  
Jacques Muller ◽  
Xiang Zhao ◽  
...  
Keyword(s):  
Crystal Structure ◽  
Physical Phenomenon ◽  
Significant Advance ◽  
Type I ◽  
Simple Method ◽  
Promising Tool ◽  
Twinning Plane ◽  
Complex Crystal Structure ◽  
Twinning Direction

The fundamental theory of crystal twinning has been long established, leading to a significant advance in understanding the nature of this physical phenomenon. However, there remains a substantial gap between the elaborate theory and the practical determination of twinning elements. This paper proposes a direct and simple method – valid for any crystal structure and based on the minimum shear criterion – to calculate various twinning elements from the experimentally determined twinning plane for Type I twins or the twinning direction for Type II twins. Without additional efforts, it is generally applicable to identify and predict possible twinning modes occurring in a variety of crystalline solids. Therefore, the present method is a promising tool to characterize twinning elements, especially for those materials with complex crystal structure.

TEM Study of (015) Growth Twins in The Bi-Sr-Ca-Cu-O Superconductors Obtained by Melt Quench Technique

1991 ◽  
Vol 238 ◽  
Author(s):  
Ohnishi N ◽  
Sankararaman M ◽  
Sato H
Keyword(s):  
Electron Microscopy ◽  
Transmission Electron Microscopy ◽  
Electron Diffraction ◽  
Grain Growth ◽  
Twin Boundary ◽  
Twin Structure ◽  
Transmission Electron ◽  
Twinning Plane ◽  
Incommensurate Modulation ◽  
New Type

ABSTRACTA new type of twin structure is found to exist quite commonly in the Bi2Sr2CaCu2O8+δ superconductor obtained by annealing melt quenched amorphous precursors. From transmission electron microscopy and electron diffraction, the twinning plane is determined to be the (015) plane (disregarding the period of incommensurate modulation in the b-direction). Further, the twin boundary is found to be coherent with a specific coincidence condition. The analysis of the morphologies indicates that the twins nucleate at the early stages of the grain growth in these materials.

Calculation Methods to Determine Crystallographic Elements Based on Electron Diffraction Orientation Measurements by SEM/EBSD or TEM

2012 ◽  
Vol 706-709 ◽  
pp. 2674-2679
Author(s):  
Yu Dong Zhang ◽  
Zong Bin Li ◽  
Claude Esling ◽  
Xiang Zhao ◽  
Liang Zuo
Keyword(s):  
Crystal Structure ◽  
Electron Diffraction ◽  
Sample Surface ◽  
Type I ◽  
Type Ii ◽  
Calculation Methods ◽  
Orientation Relationships ◽  
Prepared Sample ◽  
Twinning Plane ◽  
Twinning Direction

In the present work, we summarized two calculation methods to determine some specific crystallographic elements based on electron diffraction orientation measurements by SEM/EBSD or TEM. The first one is to determine the twin type and twinning elements of crystal twins based on the minimum shear criterion, using the experimentally determined twinning plane for Type I twin and compound twin or twinning direction for Type II twin as initial input. The method is valid for any crystal structure. The second one is one to determine the plane indices of the faceted interfaces where the orientation relationships (ORs) between the adjacent crystals are reproducible. The method requires one prepared sample surface instead of two perpendicular surfaces. These methods are expected to facilitate the related microstructural characterizations.

Preparatory Procedures for Electron Microscopic Analysis at the Molecular Level of Resolution

1978 ◽  
Vol 36 (3) ◽  
pp. 516-520
Author(s):  
F.J. Sjostrand
Keyword(s):  
Electron Microscope ◽  
Molecular Level ◽  
Microscopic Analysis ◽  
Resolving Power ◽  
Cellular Structures ◽  
Electron Microscopic ◽  
Systematic Analysis ◽  
Technical Developments ◽  
Thin Sectioning ◽  
Obvious Reason

In the 1940's and 1950's electron microscopy conferences were attended with everybody interested in learning about the latest technical developments for one very obvious reason. There was the electron microscope with its outstanding performance but nobody could make very much use of it because we were lacking proper techniques to prepare biological specimens. The development of the thin sectioning technique with its perfectioning in 1952 changed the situation and systematic analysis of the structure of cells could now be pursued. Since then electron microscopists have in general become satisfied with the level of resolution at which cellular structures can be analyzed when applying this technique. There has been little interest in trying to push the limit of resolution closer to that determined by the resolving power of the electron microscope.

The structure of amorphous and polycrystalline materials using energy-filtered RDF analysis

1992 ◽  
Vol 50 (2) ◽  
pp. 1190-1191
Author(s):  
David Cockayne ◽  
David McKenzie
Keyword(s):  
Electron Diffraction ◽  
Diffraction Pattern ◽  
Density Function ◽  
Electron Diffraction Pattern ◽  
Polycrystalline Materials ◽  
Nearest Neighbour ◽  
X Ray ◽  
Selected Area Electron Diffraction ◽  
Reduced Density ◽  
System F

The technique of Electron Reduced Density Function (RDF) analysis has ben developed into a rapid analytical tool for the analysis of small volumes of amorphous or polycrystalline materials. The energy filtered electron diffraction pattern is collected to high scattering angles (currendy to s = 2 sinθ/λ = 6.5 Å-1) by scanning the selected area electron diffraction pattern across the entrance aperture to a GATAN parallel energy loss spectrometer. The diffraction pattern is then converted to a reduced density function, G(r), using mathematical procedures equivalent to those used in X-ray and neutron diffraction studies.Nearest neighbour distances accurate to 0.01 Å are obtained routinely, and bond distortions of molecules can be determined from the ratio of first to second nearest neighbour distances. The accuracy of coordination number determinations from polycrystalline monatomic materials (eg Pt) is high (5%). In amorphous systems (eg carbon, silicon) it is reasonable (10%), but in multi-element systems there are a number of problems to be overcome; to reduce the diffraction pattern to G(r), the approximation must be made that for all elements i,j in the system, fj(s) = Kji fi,(s) where Kji is independent of s.

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